This application for an NIH R21 award under PA-03-080 (Biodefense and Emerging Infectious Disease Research Opportunities) is based on preliminary studies just recently obtained in the laboratory, and that we believe are of great interest as the basis for further exploratory studies. Our laboratory is involved in the identification of virulence determinants of Borrelia burgdorferi, the causative agent of Lyme disease. Lyme disease is considered an emerging infection because the geographic distribution and the number of cases continue to expand in North America. The ability of B. burgdorferi to disseminate from the site of inoculation, a tick bite, to multiple tissues indicates that interactions with mammalian cells occur at multiple stages of infection. In particular, the hematogenous dissemination of the spirochete to multiple tissues suggests that interactions with the vascular endothelium are critical to the ability of B. burgdorferi to cause infection. As described in this proposal, we used a filamentous phage display library of B. burgdorferi DNA in vivo to select for phage clones that exhibit tropism to the vasculature in the hearts and joints of mice. These tissues were selected for analysis because they are frequently infected by B. burgdorferi in humans and in animal models of Lyme disease. We have identified three known or predicted outer membrane proteins of B. burgdorferi as potential vascular tropism determinants: OspC, VlsE, and the as yet uncharacterized product of gene BB0210. We now propose to generate the relevant fragments of these three proteins in recombinant form, and to test the recombinant proteins for specific binding to endothelial cells. In addition, we will investigate the nature of the endothelial cell receptors for these B. burgdorferi proteins. The experiments that we are proposing will shed light on the significance of three B. burgdorferi proteins that may facilitate interactions of B. burgdorferi with the vasculature during the natural course of infection in mammals. [unreadable] [unreadable]